Magnetic field sensors have applications in magnetic compassing, ferrous metal detection, position sensing, and current sensing. They may be used to detect variations in the magnetic field of machine components and in the earth's magnetic field, as well as to detect underground minerals, electrical devices, and power lines. For such applications, an anisotropic magneto-resistive (AMR) sensor, a giant magneto-resistive (GMR) sensor, a colossal magneto-resistive (CMR) sensor, a Hall sensor, a fluxgate sensor, or a coil sensor that is able to detect small shifts in magnetic fields may be used.
MR sensors, for example, may be formed using typical integrated circuit fabrication techniques. Permalloy, a ferromagnetic alloy containing nickel and iron, is typically used as the magneto-resistive material. Often, the permalloy is arranged in thin strips of permalloy film. When a current is run through an individual strip, the magnetization direction of the strip may form an angle with the direction of current flow.
As the magnetization direction of the strip changes relative to the current flow, its effective resistance also changes. Strip resistance reaches a maximum when the magnetization direction is parallel to the current flow and reaches minimum when the magnetization direction is perpendicular to the current flow. Such changes in strip resistance result in a change in voltage drop across the strip when an electric current is run through it. This change in voltage drop can be measured and used as an indication of the change in the magnetization direction of an external magnetic field acting on the strip.
To form the magnetic field sensing structure of a MR sensor, several permalloy strips may be electrically connected together. The permalloy strips may be placed on the substrate of the MR sensor as a continuous resistor in a “herringbone” pattern or as a linear strip of magneto-resistive material, with conductors across the strip at an angle of 45 degrees to the long axis of the strip. This latter configuration is known as “barber-pole biasing.” The positioning of conductors in a “barber-pole biasing” configuration may force the current in a strip to flow at a 45-degree angle to the long axis of the strip. These magneto-resistive sensing structure designs are described in U.S. Pat. No. 4,847,584 titled “Magnetoresistive Magnetic Sensor” and assigned to the same assignee as the current application. U.S. Pat. No. 4,847,584 is hereby fully incorporated by reference.
An MR sensor often includes a number of straps through which current may be applied for controlling and adjusting sensing characteristics. For example, MR sensor designs often include set, reset, and offset straps. These straps can improve the performance and accuracy of the MR sensor, but require driver circuitry for proper operation. Additionally, the MR sensor typically includes other components used for signal conditioning and electrostatic discharge protection, such as operational amplifiers, transistors, capacitors, and so on.
An RF transceiver is commonly used to wirelessly transmit data. For example, RF transceivers are used in short range communication systems. Typically, the RF transceiver is connected to one or more antennas. When receiving data, the RF transceiver filters and down converts RF signals into analog or digital baseband signals. When sending data, the RF transceiver filters, up converts, and amplifies analog or digital baseband signals into RF signals.
By combining the functionality of the MR sensor with that of the RF transceiver, the output of the MR sensor can be wirelessly transmitted. As a result, the output of the MR sensor can be easily obtained. For example, an MR sensor may be located on a pipeline valve to determine the position of the valve (e.g., whether the valve is open or closed). The position of the valve can be wirelessly transmitted to a pipeline control station by the RF transceiver. As a result, a pipeline operator can determine the position of the valve without having to go into the field to manually determine the position of the valve.
Typically, to wirelessly transmit data from an MR sensor at least two chips are placed separately on a printed circuit board. For example, Honeywell's Radio on a Chip (part number HRF-ROC09325) along with data acquisition, data formatting, and control electronics may be used to transmit output data from one or more of Honeywell's MR sensors, such as part numbers HMC1501 and HMC1512. In some applications, multiple chips on a printed circuit board is too unwieldy and inefficient due to the physical space requirements of the RF transceiver chip, the MR sensor chip, and any additional chips required for operation of the MR sensor.
Single chip designs with an MR sensor and other additional circuitry have been described. For example, U.S. Patent Application Publication No. 2004/0207400 describes the integration of an MR sensor with a SET/RESET driver, U.S. Patent Application Publication No. 2004/0207035 describes the integration of an MR sensor with a semiconductor device, and U.S. Patent Application Publication No. 2004/0254726 describes the integration of an MR sensor with a GPS receiver. These applications are assigned to the same assignee as the current application and are hereby fully incorporated by reference. Single chip packaging for an RF transceiver has also been described. However, none of these designs suggest integrating an RF transceiver on the same chip as the MR sensor.
Thus, a single-chip design that would minimize the physical space required to integrate an MR sensor with an RF transceiver would be desirable.